Field of the Invention
The present invention relates to a method and an apparatus for controlling tyres in a tyre production line, in particular a method and an apparatus for controlling the possible presence of flaws on or in proximity to the surface of a tyre, more particularly on or in proximity to the inner and/or outer surface of the lateral walls of a tyre.
Description of the Related Art
By “tyre” it is intended the finished tyre, i.e. after the steps of moulding and vulcanisation subsequent to the building step.
Typically, a tyre has a substantially toroidal structure around a rotation axis thereof during operation, and has an axial middle line plane orthogonal to the rotation axis, said plane being typically a plane with (substantial) geometric symmetry (e.g. ignoring possible minor asymmetries, such as the design of the tread and/or the internal structure).
Two portions of the tyre are defined herein: the crown and the lateral walls. The crown comprises the tread band, the belt and the corresponding carcass structure portion, which is radially inner with respect to the former two.
By “lateral wall” it is intended one of the two portions of the tyre that are mutually facing and are radially extended on opposite sides of the crown up to the beads, i.e. up to the two radially inner end edges of the tyre, with circular extension substantially orthogonal to the rotation axis; each of said beads being intended to be coupled with a respective mounting rim. Each lateral wall thus comprises a corresponding carcass structure portion, and in axially outer position with respect thereto, a portion made of suitable elastomeric material, generally termed ‘sidewall’.
Typically, the carcass structure comprises at least one carcass ply having respectively opposite terminal flaps engaged with respective reinforcement annular structures, generally termed “bead cores”, integrated in the zones identified above with the term beads. In the tyres of “tubeless” type, the carcass ply is internally covered by a layer of elastomeric material, preferably with butyl base, usually termed “liner” having optimal characteristics of impermeability to air and being extended from one bead to the other.
Also the so-called “shoulder” is intended entirely comprised in the structure of a lateral wall; such shoulder is the portion of the tyre connecting the crown and the radially more internal portion of the lateral wall (in other words, the two shoulders correspond to the two radially and axially outer circular ‘edges’ of the tyre). The shoulder has circular extension substantially orthogonal to the rotation axis.
By homologous portions of the tyre, it is intended portions of the same component having the same geometry. For example, homologous portions are the different angular portions of the axially outer part of a lateral wall, the angular portions of surfaces of the shoulder in their circumferential extension, the corresponding liner portions inside channels or ribs determined by the expansion bladder of the mould during moulding and vulcanisation, etcetera.
By component of the tyre it is intended any one element that performs a function or a portion thereof.
By “radius of curvature” it is intended the local radius of curvature of the surface of an element of the tyre on any one radial section plane, i.e. comprising said rotation axis (given that the radial section of the tyre typically does not vary over the entire tyre).
By outer or inner surface of the tyre, it is respectively intended the surface that remains visible after the coupling of the tyre with its mounting rim and the surface no longer visible after said coupling.
The terms ‘optical’, ‘light’ and the like make reference to an electromagnetic radiation used that has at least one portion of the spectrum falling within an enlarged area of the optical band, and not necessarily strictly falling within the optical band (i.e. 400 nm-700 nm), for example such enlarged area of the optical band may range from ultraviolet to infrared (e.g. wavelength comprised between approximately 100 nm and approximately 1 μm).
By “cycle time” within a production line comprising at least one work station, preferably a plurality of work stations, and inserted in a plant for the production of tyres, it is intended, in operating conditions, the maximum transit time for a tyre being processed to cross a work station where at least a portion of a component of the tyre itself is built. For example, the cycle time can be comprised between approximately 20 and approximately 120 seconds.
In the field of the processes of production and building of tyres for vehicle wheels, the need was perceived to execute quality controls on the obtained products, with the object of preventing defective tyres from being placed on the market, and/or to progressively adjust the apparatuses and the machinery employed, in a manner so as to improve and optimise the execution of the operations performed in the production process.
Such quality controls for example include those executed by human operators who dedicate a pre-established time, e.g. comprised between 30 s and 60 s, to a visual and tactile examination of the tyre; if, in light of one's own experience and sensitivity, the operator should suspect that the tyre does not respect certain quality standards, the tyre itself is subjected to further controls, through a more detailed human control and/or through suitable equipment, for the purpose of evaluating possible structural and/or qualitative flaws in depth.
The document US 2004/0212795 describes a method for measuring the contour and/or the deformation of an object, in particular of a tyre. The object is illuminated by a light emitted by a radiation source and in particular consists of coherent or partially coherent light, especially laser light. The light reflected by the object is received by a camera with an image sensor.
The document EP0785421 describes a method for detecting anomalies in a deformable object, by means of the observation of the dynamic changes in the deformable object using light reconstruction techniques. For example, when the pressure in an object made of reinforced rubber is varied, the weakest portions of the object expand more than the areas surrounding the object. These variations can be detected, recorded and analysed.
In the field of controls on tyres, the Applicant has addressed the problem of detecting the possible presence of flaws on or in proximity to the inner and/or outer surface of the lateral walls. The flaws sought can for example be irregularities on the surface of a tyre (non-vulcanised compound, form alterations, etc.), structural non-uniformities, presence of foreign bodies on the surface. Among the structural non-uniformities, the so-called “shifting in the carcass” is particularly critical; this is a rare flaw that can also be very dangerous, generated in the region of interface between two portions of the tyre having different chemical-physical characteristics (e.g. different compounds). Such flaws present themselves as small cuts (typically with longitudinal extension, i.e. which follows the circular extension of the tyre) characterised by perfectly mating flaps (between which there is no removal or lack of material); this characteristic makes the flaws particularly hard to identify. The shifting in the carcass can also affect structures of the carcass placed in proximity to the surface of the tyre, for example in proximity to the inner surface, below the liner layer that is typically present. In such case, typically the liner itself is involved in the shifting, it too having a tear with the shifting in the carcass and hence making the identification through optical inspection possible.